Light Emitting Diodes (LEDs) are increasingly being adopted as general illumination lighting sources due to their high energy efficiency and long service life relative to traditional sources of light such as incandescent, fluorescent and halogen. Each generation of LEDs are providing improvements in energy efficiency and cost per lumen, thus allowing for lighting manufacturers to produce LED light fixtures at increasingly competitive prices.
With the exception of relatively limited AC LED modules, LED modules typically operate using DC power with the current flowing through the LEDs dictating the lumens produced. In a typical LED light fixture, an AC to DC driver is implemented to convert AC power from the power grid to DC power that can be used to power the LEDs. In some cases, a constant voltage driver is used which will maintain a particular DC voltage. This architecture can work if the DC voltage of the driver is matched perfectly with the LED modules being used to ensure an appropriate current will flow through the LEDs to produce the desired output light intensity. Perfectly matching the DC voltage output of a constant voltage driver with a particular forward voltage for a series of LEDs is not simple and could add complexity to the design of the LED modules. Further, fluctuations in the forward voltage of LEDs will occur if thermal temperature changes occur and long wires used to connect the LED modules may increase voltage drops. These fluctuations will result in load requirements changing while the constant voltage driver maintains the same voltage output, thus causing fluctuations in the current flowing through the LEDs. The result of this situation is an inconsistent light output intensity which is not desired.
To overcome the problems with the use of constant voltage drivers with LEDs, it has become typical for light fixtures to be designed using AC to DC drivers that are constant current drivers. The constant current drivers, as their name indicates, output a constant current to the attached LED modules as long as the load has an operating voltage range within the acceptable limits of the driver. For instance, a constant current driver may be set to 700 mA with an operating voltage range of 12-24V. In this case, LED modules with a forward voltage of 21V will operate with a current of 700 mA. Typical constant current drivers use a feedback control mechanism to adjust the output voltage between a high power rail and a low power rail depending upon the current that is detected.
Due to their popularity in LED light fixtures, constant current drivers are decreasing in cost at a fast rate and becoming a commodity product. Key differentiators of different constant current drivers are their efficiency, wattage and flexibility. In terms of flexibility, some designs for constant current drivers allow for their output current to be programmed in using a programming tool (either wired or wireless). In some cases, a plurality of different outputs with different current levels may be output from the constant current drivers.
One control feature that is offered increasingly as a standard control feature within constant current drivers is 0-10V dimming 0-10V dimming is a system that typically interfaces with a wall mounted dimmer and allows a user to adjust the output current of the constant current driver and therefore the light intensity of the light fixture that the constant current driver is implemented. In normal implementations, the wall mounted dimmer acts effectively as a variable resistor and the constant current driver provides a very small current between grey and purple dimming wires that connect through the dimmer to detect a voltage drop. The level of the voltage drop can determine a desired dim level for the constant current driver. As a result, the constant current driver can adjust the desired output current to be provided to attached LED modules.
A problem with the commoditization of the constant current drivers is that there is little development on how to implement advanced control features using these simple AC to DC converters. Technologies have developed in lighting to allow for a wide range of control features to lower energy usage, increase user experience and/or communicate information to/from light fixtures. None of these features can easily be implemented using the simple constant current drivers that are becoming the standard components in LED light fixtures.
Against this background, there is a need for solutions that will mitigate at least one of the above problems, particularly enabling additional control features to be implemented using standard constant current drivers.